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What is an IQ Test?

IQ or Intelligence Quotient is an attempt to measure intelligence. This means many things to many people but generally the attribute of intelligence refers to quickness of mental comprehension (or mental agility).

Intelligence is often confused with knowledge, wisdom, memory, or other attributes and in general has a variety of meanings depending on the context in which it is used. The term IQ usually refers to the attempt to measure a person's mental agility. There are many standard IQ tests in use around the world. On most intelligence tests, average IQ score is 100, but some tests give different numerical values to the level required for entry into Mensa, in the same way that the same temperature is expressed by different numerical values on the Fahrenheit and Celsius scales.

One way of comparing scores from different IQ tests is to convert them to a ranking, or percentile score, which tells you in which band you fit. A percentile score of 99% means that you are in the top 1%, a percentile score of 98% puts you in the top 2% and so on.

British Mensa uses two main tests to identify people's IQ scores, the Cattell III B and the Cattell Culture Fair III A. A score which puts you in the top two per cent of the population on either of these papers would qualify you for membership of Mensa. An adult can only get a maximum IQ of 161 on the Cattell III B test and 183 on Culture Fair.

A top two per cent score on Cattell III B would be 148 or over, while for Culture Fair it is 132 or over.

The two papers test different types of IQ. Cattell III B includes a lot of verbal reasoning, while Culture Fair - as the name suggests - is more suitable for people for whom English is not their first language and for those with language processing problems such as dyslexia. It has no words, only diagrams and images.

Comparison of IQ Tests
As different IQ tests were developed, each was given its own scoring system. Therefore, an IQ of 150 is a meaningless claim unless you know the actual test which was used. In order to compare one IQ test against another, the scores are converted to 'percentiles', i.e. where a person's score falls in comparison to the rest of the population by percentage. Mensa offers membership to anyone whose IQ score places them within the top two per cent of the population, no matter which approved test was used.

Note: The absolute score on any given IQ test which equates to the 98th percentile varies, once test scores are constrained to a normal distribution a direct comparison between tests can be made. For prior evidence we look at tests individually and take the 98th percentile as set out in the technical manual for the particular version of a test taken.